1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing a hermetic coating optical fiber, and more particularly to such a method and an apparatus suitable for mass production.
2. Related Background Art
A hermetic coating for an optical fiber is effective to prevent ambient gases such as water, hydrogen etc. from adhering to the optical fiber or permeating through the optical fiber. Generally, inorganic materials such as metals including alloys and carbon etc. are used as coating materials. Above all, carbon coating is one of the most excellent ones in term of its chemical stability and fine grained structure etc. and one of the coating processes is chemical vapor deposition (CVD) process in which reactant gas reacts chemically to deposit coating material on the optical fiber surface, because it is advantageous in terms of coating speed and quality of the layer.
Conventional apparatuses for performing the above mentioned technologies, are described, for example, in U.S. Pat. No. 4,790,625 or European Patent Application No. 0,308,143. In those apparatuses or methods, the reactor vessels typically have a seal gas inlet port, reactant gas inlet port and waste gas discharge port from the upper to the lower. And a formed fiber of high temperature is hermetic-coated thermo-chemically in the reactor vessel between the reactant gas inlet port and the waste gas discharge port.
Usually in those processes, an optical fiber is drawn from a preform in a draw furnace, before it is provided with hermetic coating. The temperature (about 1300.degree. C.) necessary for formation of the coating particles at the fiber surface maintained at the fiber surface without the need for additional heating means.
In those conventional apparatuses, solid particles such as carbon generated in a vapor phase tended to be deposited on the inner wall, of the reactor vessel. When a fiber was tried to be coated in a long length, the solid particles gradually are deposited on the inner wall of the reactor vessel so that the vessel is clogged in a long period of time requiring the process. Consequently, fiber forming becomes impossible. Without solving the problem, a yield rate of the optical fiber could not be improved and high productivity could not be attained.